Some products, such as solar control window films and security markings, would benefit from colorless or nearly colorless layers that have strong reflectance in the infrared region so that the products can reflect or block the infrared region of sunlight or, in the case of security markings, can be read by an infrared scanner or camera, but do not provide enough of a visible image to be easily noticed by humans or detected by a visible scanner or camera. For example, U.S. Pat. No. 7,151,626, to Carlson, and U.S. Pat. Pub. Applic. No. 20070097510, to Carlson et al., describe solar control window films comprising aminium radical cation compounds that exhibit high levels of reflectance in the infrared region while having very little visible color. Also, for example, U.S. Pat. Nos. 6,381,059; 6,589,451; and 7,151,626, all to Carlson, describe infrared layers for security markings that comprise an aminium radical cation compound and are capable of being detected in the infrared region while being invisible or nearly invisible to the human eye or to detection by a visible scanner.
It would be advantageous if such infrared reflective layers were highly stable in the intensity level of their infrared reflectance and in their level of visible coloration upon extended exposure to light, heat, and humidity and, when combined directly with other layers by coating or lamination, retain their level of infrared reflectance and their stability against discoloration or degradation. It would be further advantageous if stable and low color infrared absorbing layers that have too much heat buildup by themselves to be effective in solar control window films, due to the possibility of breaking the window by excessive and rapid heat buildup by the sun, could be utilized in solar control window films.
Solar control window films must typically contain a significant amount of infrared reflectance and not depend primarily on infrared absorption to block the sun's infrared radiation. The disadvantage of blocking sunlight by mainly infrared absorption is that the absorbed sunlight is converted to heat in the solar control window film, and much of this heat diffuses into the building, vehicle, or other structure with the solar control window films on the windows. Infrared reflection has the significant advantage of reflecting the sun's infrared energy back into the atmosphere.